The present invention relates to improved stomach-action molluscicides. stomach poisons or edible baits containing them and their use in killing, controlling and/or inactivating molluscs, in particular, slugs and snails. More particularly, the present invention relates to a stomach-action molluscicide containing at least one additive, which is specifically included to increase the efficacy of such a molluscicide and which lowers the cost of production of such a molluscicide.
Slugs and snails are major pests of agriculture in many parts of the world. The ecologies of different types of molluscs, which can be either terrestrial or aquatic, are very different and they usually require different types of treatment. The snail species, Cepaea hortensis, Theba pisana, Helix aspersa, Cernuella virgata and Achatina spp and the slug species, Deroceras reliculatum, Arion hortensis, Milar budapestensis and Limax maximus are of particular interest as targets. The common garden snail, Helix aspersa and the grey field slug, Deroceras reticulatum, are common garden pests throughout Australia. On the other hand, there are groups of snails, which have been introduced into Australia in the twentieth century that are ever increasing in number. These are the white Italian snail, Theba pisana, and the vineyard or Mediterranean snail, Cernuella virgata, which both cause extensive crop damage.
Significant crop damage by molluscs also occurs in northern Europe, the Middle East, North and Central America, South East Asia, Japan and New Zealand. In many cases, the rise to pest status of the slug or snail in question is a consequence of changexe2x80x94either in distribution (as in the case of accidental or deliberate introductions) or in agricultural practice, where crops or systems of cultivation may enable populations to rise to pest levels. Slugs are a major agricultural pest which cause significant crop damage by burying themselves in the soil and then moving along into holes drilled for planting new crop seeds in. Once the seed has been placed in the drill holes, they eat the inside out of the new seed, thereby potentially destroying the whole planting.
Chemical methods (i.e. the use of molluscicides), involving the use of stomach poisons for the control of such pests, are well known. Molluscicides containing metaldehyde and methiocarb have been in use for some while. The use of metal complexes in stomach-action molluscicides was first proposed by Henderson et al. in xe2x80x9cAluminium(II) and Iron(III) complexes exhibiting molluscicidal activity,xe2x80x9d Australian Patent AU-B-22526/88. In one of their studies, these workers compared the relative toxicities of some aluminium and iron salts and chelates and their efficacies as stomach poisons, by injecting known amounts into the gut lumen of molluscs and they found that, in fact, the metal chelates were more toxic than their corresponding salts. Metal chelates were also first trialed by Henderson et al as contact-action poisons. In one particular study, Henderson used the metal chelate, FeEDTA, as the toxic agent, finding it just as effective as various salts of Fe(III). (Henderson, I. F. et al, in xe2x80x9cA New Group of Molluscicidal Compounds,xe2x80x9d BCPC mono., (1989), 41, xe2x80x9cSlugs and Snails in World Agriculturexe2x80x9d, pp 289-294 eds. Henderson, I. F., British Protection Council, Farnham, U. K.).
More recently, Puritch el al in xe2x80x9cIngestible Mollusc Poisons,xe2x80x9d International Patent Application No. WO 96/05728 claimed a terrestrial mollusc stomach poison containing, as the active ingredient, either ferric edetate or the ferric hydroxy-ethyl derivative of edetic acid. These workers have also shown that mixtures of iron salts such as ferric sulphate, ferric chloride or ferric nitrate when mixed together with disodium EDTA or EDTA, as such, are toxic to the slug species, Deroceras reliculatum. 
The term xe2x80x9cstomach-action molluscicidexe2x80x9d is used herein in its broadest sense and includes a molluscicide, which is capable of being ingested into the stomach of the mollusc in an effective amount so as to kill and/or inactivate the mollusc.
The term xe2x80x9cmetal complexonexe2x80x9d is used in its broadest sense and refers to a chelate of a metal with at least one ligand of the complexone type. The term xe2x80x9ccomplexonexe2x80x9d as used herein refers to an organic ligand containing at least one iminodiacetic group xe2x80x94N(CH2CO2H)2, or two aminoacetic groups xe2x80x94NHCH2CO2H2, or a derivative of either of these where the xe2x80x94CH2 group is substituted, which form complexes with most cations. Suitable complexones include those disclosed in Wilkinson, G., xe2x80x9cComprehensive Coordination Chemistry,xe2x80x9d Volume 2, Chapter 20.3, pp 777-792 which is incorporated herein by reference.
In general, most toxic compounds are also repellent and the interaction of toxicity with repellency prevents the ingestion of sufficient poison to kill the mollusc. Therefore, the essential problem that an effective stomach-action molluscicide has to overcome is that of palatability since in order for it to be effective, it must be ingested by the mollusc. Although Puritch et al claimed that their formulations provide a palatable molluscicide, indeed tests carried out on these formulations by the present inventor revealed the acidic, and hence possibly unpalatable, nature of these formulations. It is believed that a significant proportion of the efficacy, claimed by Puritch et al, is possibly due to the molluscicidal formulation of either ferric edetate or the ferric hydroxy-ethyl derivative of edetic acid, or indeed, mixtures of iron salts, such as ferric sulphate, ferric chloride or ferric nitrate, when mixed together with disodium EDTA or EDTA, acting as a contact poison rather than an ingestible poison. It is further believed that the claimed palatable nature of these formulations arises not so much from the inclusion of the specific active ingredient, but rather from the elements of the xe2x80x9cinertxe2x80x9d carrier containing bran/flour and a phagostimulant, which would cause the bait to be sufficiently palatable to allow ingestion.
The present inventor therefore initially sought to develop a molluscicide, wherein the active ingredient itself was more palatable, efficacious and also one which was not harmful to the environment. In this, the present inventor was successful and developed and made an application for a patent, International Patent Application No: PCT/AU97/00033, for a stomach-action molluscicide, containing the hydroxy compound, [Fe(OH)EDTA]2xe2x88x92 or its dimer, [EDTA-Fexe2x80x94Oxe2x80x94Fe-EDTA]4xe2x88x92 as the active ingredient, which was found to be more palatable to molluscs and therefore also more efficacious.
The present inventor serendipitously discovered that the addition of K2CO3 or CaCO3 as a filler to a molluscicidal bait containing FeEDTA, resulted in a bait that was more effective than with no additional filler being added. These fillers also fortuitously acted as pH adjusters which effectively adjusted the pH of the bait to around 8. At low pH, the Fe(III) atom in FeEDTA is surrounded by the two nitrogen atoms and the four oxygen atoms, provided by the hexadentate ligand, EDTA, and a water molecule acting as an additional seventh donor ligand. At a pH above 7, the water molecule is replaced by either an xe2x80x94OH group or an xe2x80x94Oxe2x80x94 group. At a pH of between 7 and 10, the species present in the majority are [Fe(III)(OH)EDTA]2xe2x88x92 or its dimer, [EDTA-Fexe2x80x94Oxe2x80x94Fe-EDTA]4xe2x88x92 with Fe(III)EDTA being present in the minority. The hydroxy compound and its dimer are in equilibrium, the relative amounts depending on the moisture of the pellet. According to F. G. Kari et al, Environ. Sci. Technol., (1995), 29, 1008, at a pH of about 8 to 8.5, there is virtually no Fe(III)EDTA present at all. The present inventor has found that molluscicides having a pH of greater than 7, but less than 9 or 10 appear to be more palatable than those having a pH of 7 or below. In addition, at higher pH, the Fe(III) ions are more readily replaced bv Ca2xe2x88x92ions, liberating the Fe(III) ions for passage through the intestinal epithelium into the blood stream. It is suggested that these Fe(III) ions may then complex with haemocyanin present as the oxygen-carrier in the blood of the mollusc, in some as yet unexplained way, resulting in an inhibition of the oxygen uptake by the mollusc, leading to its eventual death.
A further essential requirement for an efficacious stomach-action molluscicide is that premature termination of feeding must not result so that an insufficient amount of poison is ingested to kill the pest. In this way, the molluscicide needs to be more than a feeding deterrent or a crop protectant. One way of achieving this is to increase the concentration of active ingredient present in the bait. However, this leads to excessive costs of production and to a bait that is more harmful to non-target animals. This latter consideration is of particular concern since stomach-action poisons are often consumed by non-target organisms such as domestic animals, birds and children, particularly when baits are used. There is always a possibility that the bait will be consumed by such non-target organisms. Accordingly, the present invention seeks to improve the efficacy of the bait in such a way as to further decrease its harmful effects on non-target organisms.
Surprisingly, the present inventor has now found that the addition of surfactant to the molluscicidal formulation disclosed in International Patent No. PCT/AU97/00033 provides significant advantages over that formulation. Surfactants are principally known as agents, which reduce the surface tension of liquids and have been particularly widely used in the detergent industry. Surfactants have also been used in the molluscicidal industry, but principally for their emulsifying characteristics (Albright and Wilson, Patent No. GB 2 252 499 A, (1992)) and to facilitate the milling process of the molluscicide (Tavener et al, Patent No. AU91178623). Henderson et al have shown that the efficacy of stomach-action molluscicides, containing metaldehyde and methiocarb, both highly toxic active ingredients, can be increased by the addition of small amounts of additives (Henderson et al, Ann. appl. Biol., (1992), 121, 423-430); (Bowen et al, Patent No. GB 2098 869 A, (1982) and Bowen et al, in BCPC Symposium Proceedings, (1996), 66, xe2x80x9cSlug and Snail Pests in Agriculture,xe2x80x9d pp397-404).
A number of surfactants in the form of their aqueous solutions were claimed to have molluscicidal activity on aquatic snails. (Visser, S. A., Bull. Wld. Hlth. Org., (1965), 32, 713-719). Visser found that aqueous solutions of cationic detergents were on the whole more toxic than the anionic or non-ionic detergents used as aqueous solutions. Dawson et al, in BCPC Symposium Proceedings, (1996), 66, xe2x80x9cSlug and Snail Pests in Agriculture,xe2x80x9d pp 439-444, eds. Henderson, I. F., British Protection Council, Farnham, U. K.) have investigated the repellency of a range of surfactants to the slug, Deroceras reticulatum. They found that in particular, tetraammonium salts were highly repellent and some polyphenylpolyethoxylates were also repellent with the degree of repellency varying with the degree of ethoxylation. These workers were interested in using surfactants as a repellent to crops. Their laboratory tests showed that crawling slugs rapidly detect and are deterred by topical applications of chemicals at low deposit rates. They concluded that surfactants were of limited use in this type of application, since they were rapidly removed from the plant by rain and by condensation.
Selected surfactants are considerably less toxic to mammals than others. Sodium dodecyl sulphate (SDS) is a surfactant, which is widely used as an emulsifier in agricultural chemicals. It is a popular choice amongst surfactants, since it is biodegradable and is generally regarded as being environmentally safe. Tseng et al, in Proceedings of the National Science Council, R. O. C., Part B: Life Sciences, Vol. 18, No. 3, (1994), pp 138-145, found that sodium dodecyl sulphate (SDS) was an effective molluscicide, when used on its own at a concentration of 100 ppm, for the semi-aquatic golden apple snail, Pomacea canaliculata. SDS was used in this case as an aqueous solution applied onto the water surface. Tseng et al also observed that snail movement and vital response stopped sooner at an acidic pH compared with at an alkaline pH. These workers believed that the molluscicidal activity of SDS appeared to be due to xe2x80x9cdermalxe2x80x9d absorption, rather than as an xe2x80x9coralxe2x80x9d (stomach) poison.
However, although the use of surfactants have been studied in the past, the synergistic effects of surfactants with metal complexones in molluscicidal formulations or compositions have not been previously studied.
The present inventor found that several surfactants, tested under the experimental conditions leading to the present invention, exhibited no efficacy when used on their own on terrestrial molluscs. Accordingly, experiments were designed wherein the surfactant was employed in combination with a known stomach poison and it was found that a synergism exists between the metal complexone and the surfactant. The inclusion of surfactants as the synergistic additive in stomach-action poisons, in accordance with the present invention, offers considerable advantages over the presently known stomach-action molluscicides. Since it was believed that the surfactant would exhibit a synergistic effect with the metal chelate, its inclusion in the composition might enable the amount of metal chelate utilised in the composition of the bait to be reduced. Not only would this further reduce the harmful effects of the molluscicide on non-target organisms, but also, since less metal chelate would be required to produce the same level of efficacy, the inclusion of the surfactant might significantly lower the cost of production.
It is well known that the inclusion of the poison in a bait, as a pellet, gives significantly better results than the direct application of molluscicide lo the soil or application of the bait as a powder to the soil. Details of bait formulation in the prior art have generally been given without discussion of differences that might be expected from other formulations. Such differences are most probably significant in determining the amount of chelate required for effective control. Indeed, it is now believed by the present inventor that some of the ferric ions of the active ingredient, [EDTA-Fexe2x80x94Oxe2x80x94Fe-EDTA]4xe2x88x92 actually react with the phytates or other natural chelating agents present in bran, a major component of the bait composition, making them unavailable for toxic action. Investigations were consequently carried out as to the effect of the addition of an additional source of Fe(III) ions to the composition of the bait, with the belief that such addition would further increase the efficacy of the bait. A further consideration to this aspect of the present invention is the quality of the bran used in the composition. Fine, low-quality bran is relatively inexpensive, but use of this type of bran leads to a low rain-resistant pellet. On the other hand, extremely fine bran, known as xe2x80x9cpasta bran,xe2x80x9d coupled with appropriate water-resistant additives can lead to a highly rain-resistant pellet. This latter alternative can be expensive and can, in fact, be more expensive than the total cost of all the other ingredients of the formulation. Since the amount of bran used in the formulation as a proportion of the total weight of the bait is considerable, the higher the percentage of bran, the higher the cost of production of the bait. It was believed that by increasing the amount of surfactant added, due to the synergistic effect, the amount of FeEDTA required might be lowered. As discussed above, since a percentage of added FeEDTA is removed from being available for molluscicidal activity by complexing with phytates or other natural chelators present in the bran, by lowering the amount of bran used, a higher percentage of FeEDTA is available for toxic action. Additionally, the cost of production would be lowered since the amount of bran is reduced. However, it was believed that a reduction in the amount of bran used might lower the attractiveness of the bait to the molluscs, since the bran is a major component affecting the palatability of the bait and therefore a balance between all these competing factors was required to be established.
Additional studies were therefore aimed at further lowering the amount of FeEDTA required for an effective kill rate and hence providing a molluscicide that was more cost effective to produce. Thus, experimental trials were designed where FeEDTA, in combination with an additional source of iron, were incorporated into the bait formulation.
Accordingly, it is an object of the present invention to combine the requirements of palatability of the molluscicide so that the poison is readily ingested, with the requirements of an effective amount of available Fe(III) ions, together with at least one additive that will increase the rate of absorption of the poison. It is also an object of the present invention to incorporate an additive, which complements and enhances the existing environmentally-friendly aspects of the use of the active ingredient, [Fe(III)(OH)EDTA]2xe2x88x92 or in the form of its dimer, [EDTA-Fexe2x80x94Oxe2x80x94Fe-EDTA]4xe2x88x92. In addition, the present invention provides a palatable, efficacious molluscicide, which is also less expensive to produce.
According to one aspect of the present invention, there is provided a stomach-action molluscicide including an effective amount of a metal complexone, an effective amount of at least one additive, excluding a metal carbonate, for enhancing the molluscicidal activity of the metal complexone, and a suitable non-liquid carrier therefor, wherein the metal of the metal complexone is selected from the group consisting of Group 2 metals, transition metals or Group 13 metals.
Preferably, the metal of the metal complexone is a transition metal. More preferably, the metal is selected from the group of iron(II) or iron(III), aluminium or copper. Most preferably, the metal is iron(III) or copper(II). Preferably, the complexone is ethylenediaminetetra-acetic acid or hydroxyethylethylenediaminetriacetic acid.
Preferably, the metal complexone is selected from the hydroxy-metal complexone, [Fe(III)(OH)EDTA]2xe2x88x92, its dimer [EDTA-Fexe2x80x94Oxe2x80x94Fe-EDTA]4xe2x88x92, or FeHEEDTA.
In a preferred form of the invention, the additive is a surfactant, wherein the surfactant is selected from the group of cationic, anionic or non-ionic surfactants. More preferably, the surfactant is anionic or non-ionic. Most preferably, the anionic surfactant is selected from the group comprising sodium dodecyl sulphate (SDS), calcium benzyl dodecyl sulphate (ALKANATE CS(copyright)) or ammonium dodecyl sulphate (ADS), but is in no way limited to these. Even more preferably, the surfactant is sodium dodecyl sulphate (SDS). When the surfactant is non-ionic, it is most preferably selected from the group of SPAN-type surfactants, comprising sorbitan monostearate and sorbitan monooleate.
Typically, the amount of surfactant required for efficacy is between about 0.05-1% of the weight of the molluscicide. Preferably, the amount is between about 0.1-0.4% by weight of the molluscicide. Most preferably, the amount is about 0.2% by weight of the molluscicide.
Typically, when used in combination with a surfactant, the amount of metal complexone required for efficacy is between about 3-7% by weight of the molluscicide. Preferably, the amount is between about 3-5% by weight of the molluscicide. Most preferably, the amount is about 3.5% by weight of the molluscicide.
In a preferred form of the invention, the non-liquid carrier for the metal complexone usually includes a mollusc food, such as a cereal, wheat flour, bran, arrowroot or rice flour, carrot, beer, rice hulls, comminuted cuttle fish, starch or gelatin, so that the mollusc is attracted to the edible bait. Non-nutrient carriers of interest include non-nutrient polymeric materials, pumice, carbon and materials useful as carriers for insecticides. The poison or bait may also contain other additives known in the art, such as mollusc phagostimulants, for example, sucrose or molasses; lubricants, such as calcium or magnesium stearate, talc or silica; binders which are suitably waterproof, such as paraffin wax, white oil or casein and flavouring agents such as BITREX(copyright) (a registered trade mark), which imparts a bitter taste and renders the poison or bait less attractive to non-target organisms and children. In order to inhibit deterioration of the poison or bait, preservatives such as sodium benzoate, vitamin E, alpha-tocopherol, 4-nitrophenol, ascorbic acid, methyl paraben, propyl paraben or sodium bisulfite may also be included.
Preferably, the waterproofing agent is selected from Guar gum, Lotus bean gum or a fatty acid alcohol. Typically, where the waterproofing agent is a fatty acid alcohol, this is present in an amount about between 1-5% by weight of the molluscicide. More preferably, the fatty acid alcohol is selected from the group of C16-C18 fatty acid alcohols. Most preferably, the C16-C18 fatty acid alcohols comprise about 2% by weight of the molluscicide and the C16-C18 fatty acid alcohol is HYDRENOL MY, which is a mixture of hexadecanol, heptadecanol and octadecanol.
To increase the density of the actual mixture before pelletising to reduce the airborne content and thus wastage of the mixture, a filler is added to the carrier. Preferably, the filler contains calcium or magnesium ions to assist in the replacement of iron in the metal complexone of the active ingredient. Typically, the filler is selected from CaCO3K2CO3, MgCO3, or a combination of these, or CaSO4, but is not limited to these. More preferably, the filler is a metal carbonate, which is present in a sufficient amount so that the pH is non-acidic. Typically, the poison or bait contains about 1-5 wt % of a metal carbonate as a filler. When the metal carbonate is CaCO3, the preferred concentration is about 2-3% by weight of the molluscicide. When the metal carbonate is K2CO3, the preferred concentration is about 4-5% by weight of the molluscicide. When the metal carbonate is MgCO3, the preferred concentration is about 0.5-5% by weight of the molluscicide.
Serendipitously, such a metal carbonate additionally acts as a pH adjustment agent and it was found that the efficacy of the molluscicide generally increased with an increase in pH up to a pH of about 10. At a pH of about 10, it was found that feeding was deterred. It was found, through trials which were carried out using various amounts of CaCO3, MgCO3 and K2CO3 combined, that a balance needs to be struck between the pH and the attractiveness of the bait to the molluscs. If the pH of the bait is too low, it has been found that the efficacy is significantly reduced. Preferably, the pH of the molluscicide is non-acidic. Typically, the molluscicide has a pH of about 7 and not exceeding 10. Preferably, the pH of the molluscicide is about 8. Preferably, the pH adjustment agent is CaCO3 or MgCO3. The amount of metal carbonate added largely depends on the other constituents present in the formulation. In general, a stomach poison having a neutral or alkaline pH, has proved to be more efficacious than one having an acidic pH. The K2CO3, CaCO3 or MgCO3 used as a filler and which adjusts the pH to about above 8, aids in the formation of the metal complexone, [Fe(OH)EDTA]2xe2x88x92 or its dimer, [EDTA-Fexe2x80x94Oxe2x80x94Fe-EDTA]4xe2x88x92. The relative amounts of each of the two different forms of the active ingredient will be determined by the amount of moisture present in the pellet.
According to another aspect of the invention, when the metal complexone is the hydroxy-metal complexone, [Fe(III)(OH)EDTA]2xe2x88x92 or in the form of its dimer, [EDTA-Fexe2x80x94Oxe2x80x94Fe-EDTA]4xe2x88x92, the molluscicide further includes additional Fe(III) ions added to the bait composition to ensure that an effective concentration of Fe(III) ions is present in the bait. Such addition of Fe(III) ions is to counteract the binding of Fe(III) with the phytates present in the bran or flour present in the carrier, thereby allowing maximum efficacy of the poison. Preferably, the additional Fe(III) ions are added in the form of a ferric salt or in the form of a clay to the composition of the bait. Typically, the clay employed is both one which contains a high concentration of Fe(III) and in the form which is suitable for use in the pelletiser. Preferably, the clay is a form of terracotta clay. More preferably, the clay is in the form of a powder.
Preferably, when the additional Fe(III) ions are added in the form of a ferric salt, the ferric salt is ferric orthophosphate. Typically, the amount of ferric orthophosphate required for efficacy is between about 1-5% by weight of the molluscicide. Preferably, the amount required is between about 1-3% by weight of the molluscicide.
Typically, when in combination with an effective amount of an additional source of iron and an effective amount of metal carbonate, the amount of metal complexone required for efficacy is between about 1-9% by weight of the molluscicide. Preferably, the amount is between about 2-3% by weight of the molluscicide. Most preferably, the amount is about 2.5% by weight of the molluscicide.
In a preferred embodiment, the additive is a surfactant in combination with an additional source of ferric ions. More preferably, the molluscicide includes a metal complexone, a surfactant, an additional source of ferric ions and a metal carbonate. Most preferably, the molluscicide includes an effective amount of FeEDTA, an effective amount of sodium dodecyl sulphate (SDS), an effective amount of ferric orthophosphate and an effective amount of calcium carbonate. Most preferably, the amount of FeEDTA is 2-3% of the weight of the molluscicide, the amount of SDS is about between 0.1-0.2% of the weight of the molluscicide, the amount of ferric orthophosphate is between about 1-2% of the weight of the molluscicide and the amount of calcium carbonate is between about 3-4% of the weight of the molluscicide.
The molluscicide is advantageously presented in a solid form such as tablets, a powder, granules or pellets. Those skilled in the art will appreciate that it is preferable to prepare the products, which are the subject of the invention, in a form that is easy for consumers to use. Pellets, for example, can be easily scattered from a box across the area to be protected. Preferably, the molluscicide is in the form of a pellet. More preferably, the pellet is between 1 and 4 mm long and less than 3 mm in diameter. Most preferably, the pellet is 1.5 mm long and 1.5-2.0 mm in diameter.
It is to be understood by those skilled in the art that the scope of the present invention includes the stomach-action molluscicide disclosed herein, when used in combination with at least one other molluscicide.
According to another aspect of the invention, the method of preparation of the stomach-action molluscicide in pellet form includes the steps of:
(i) blending the components together to form a blended composition;
(ii) heating the blended composition for about 1 to 5 minutes in the-presence of steam at an ambient temperature of between about 80xc2x0 and 100xc2x0 C.;
(iii) maintaining the composition at the ambient temperature between about 10 and 30 seconds; and
(iv) forming the blended composition into one or more pellets.
Preferably, step (ii) is carried out at about 90xc2x0 C. for about 2 minutes, whereafter step (iii) is carried out for about 15 seconds. Preferably, the blended composition is formed into pellets under pressure. Throughout this specification and the claims which follow, unless the context requires otherwise, the word xe2x80x9ccomprise,xe2x80x9d or variations such as xe2x80x9ccomprisesxe2x80x9d or xe2x80x9ccomprising,xe2x80x9d will be understood to imply the inclusion of a stated integer or group of integers but not to the exclusion of any other integer or group of integers.